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When the fires end. 6-May-2003 At 10:40:34 AM Nico
I re-discovered the press release from Geoscience Australia: here it is:

Bushfires give rocks facelift

For immediate release, Tuesday 29th April 2003

Geoscience Australia scientists have confirmed that granite boulders in Canberra's forests have shed their skins as a result of the bushfires which swept through much of the ACT in January this year.

Teachers were baffled to find new faces on many of the granite boulders on the fire-ravaged hills surrounding Birragai Outdoor School. They called in experts from Geoscience Australia to work out what was happening.

"As the intense bushfires passed over the landscape, they heated the surface of the granite boulders to above 500 degrees Celsius. This caused the outside of the boulders to expand faster than the insides," says Greg McNamara, a geologist from Geoscience Australia.

"The expansion caused cracks to form, and just like an onion, the outside layers fell away from the rocks exposing freshly exfoliated granite faces".

"The old surfaces of some of the boulders have exfoliated as flakes about the size of roof tiles, while the surfaces of other boulders have fallen off in chunks the size of coffee tables".

"This type of weathering is most common in granites and granite-like rocks, which make up a fair proportion of Australia's landscape. With Australia being bushfire prone, exfoliation may account for more weathering than was previously believed", adds Mr McNamara.

"Where we once thought exfoliation of granite boulders occurred over hundreds of years, in reality it may have occurred over just a few months following an intense bushfire".

Exfoliation is a type of weathering that chemically and mechanically breaks down rocks and changes their composition. Weathering releases elements which are then incorporated in regolith - the soft materials, including soil, which cover hard rock.

Geoscience Australia conducts research into weathering and regolith, particularly as it affects signs of mineral deposits, and the impact it has on land degradation and salinity.


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